Simultaneously Constructing Active Sites and Regulating Mn–O Strength of Ru‐Substituted Perovskite for Efficient Oxidation and Hydrolysis Oxidation of Chlorobenzene

Abstract Chlorinated volatile organic compounds (CVOCs) are a class of hazardous pollutants that severely threaten environmental safety and human health. Although the catalytic oxidation technique for CVOCs elimination is effective, enhancing the catalytic efficiency and simultaneously inhibiting the production of organic byproducts is still of great challenge. Herein, Ru‐substituted LaMn(Ru)O3+ δ perovskite with Ru–O–Mn structure and weakened Mn–O bond strength has been developed for catalytic oxidation of chlorobenzene (CB). The formed Ru–O–Mn structure serves as favorable sites for CB adsorption and activation, while the weakening of Mn–O bond strength facilitates the formation of active oxygen species and improves oxygen mobility and catalyst reducibility. Therefore, LaMn(Ru)O3+ δ exhibits superior low‐temperature activity with the temperature of 90% CB conversion decreasing by over 90 °C compared with pristine perovskite, and the deep oxidation of chlorinated byproducts produced in low temperature is also accelerated. Furthermore, the introduction of water vapor into reaction system triggers the process of hydrolysis oxidation that promotes CB destruction and inhibits the generation of chlorinated byproducts, due to the higher‐activity *OOH species generated from the dissociated H2O reacting with adsorbed oxygen. This work can provide a unique, high‐efficiency, and facile strategy for CVOCs degradation and environmental improvement.


Supplementary Experiments
Catalysts Synthesis: For the preparation of LaMnO 3+ perovskite (LMO), quantitative lanthanum nitrate (0.03 mol) and manganese nitrate (0.03 mol) were dissolved in requisite amount of deionized water under vigorous stirring. Then citric acid and ethylene glycol were added into the homogeneous solution, and the molar ratio of metal cations: citric acid: ethylene glycol is 1: 1.5: 3. Afterwards, the solution was evaporated at 80°C to produce a viscous gel, followed by drying at 100°C overnight. The spongy material, after grinding, was calcined at 200°C for 1 h and 750°C for 4 h with the heating rate of 1°C/min. The similar procedure was used to synthesize LaMn 0.98 Ru 0.02 O 3+ (LMRO) except that aforementioned 0.003 mol manganese nitrate was replaced by 0.0294 mol manganese nitrate and 0.0006 mol ruthenium nitrosyl nitrate. As for the preparation of Ru/LaMnO 3+ (Ru/LMO), a wet impregnation route was used, where 1g LMO was mixed with 20 mL ruthenium nitrosyl nitrate solution (the concentration is 1.5% w/v Ru) for 2 h, then the suspension was evaporated by a rotary evaporator. Finally, the solid was dried at 80°C followed by calcination at 450°C for 4 h.
Catalysts Characterization and DFT Calculation: X-ray diffraction (XRD) patterns of catalysts were obtained on a Bruker XRD D8 Advance X-ray diffractometer with Cu K radiation (40 kV and 40 mA). The practical contents of Ru were measured by inductively coupled plasma-optical emission spectrometer (ICP-OES) technique using an Agilent ICPOES730 spectrometer. The nitrogen adsorption-desorption isotherms were recorded on an ASAP 2020 PLUS HD88 instrument at the temperature of 77 K, and the samples were pretreated at 300°C for 3 h before analysis. The specific surface area was measured by Brunauer-Emmett-Teller (BET) model. Electron paramagnetic resonance (EPR) spectra were obtained on an electron paramagnetic resonance spectrometer (Bruker, E500) at room temperature.
Aberration-corrected high-angle annular dark filed scanning transmission electron microscopy (AC-HAADF-STEM) was performed at 200 kV on a JEOL JEM-ARM 200F electron microscope equipped with an EDS detector. The data of electron energy loss spectroscopy (EELS) was acquired on a matched spectrometer for the analysis of electronic structures and chemical compositions. X-ray photoelectron spectroscopy (XPS) analysis were -ray source and binding energies were calibrated with the C1s peak at 284.6 eV.
The structures of samples were examined by Raman spectroscopy (Renishaw inVia confocal Raman) with the use of 532 nm -1 laser light. Ex-situ Raman spectrum were measured at room temperature. In-situ Raman spectrum were measured under different temperatures in an in-situ reaction cell. Before the CB oxidation test, the catalyst was pretreated by 21% O 2 /N 2 at 400 ℃ for 1 h and then cooled to 200°C. The reactant gas was identical with catalytic performance measurement, which consisted of 500 ppm CB and 21% O 2 /N 2 . Mn Kedge extended X-ray absorption fine spectra (EXAFS) were performed at 1W1B station in Beijing Synchrotron Radiation Facility (BSRF). The storage rings of BSRF were operated at 2.5 GeV with a maximum current of 250 mA. The Si (111) double-crystal monochromator was used to detect the signal which were carried out in transmission mode in ionization chamber. All spectra were collected in ambient conditions. The EXAFS data were analyzed by the Artemis module of IFEFFIT software packages. First, k 3 -weighted EXAFS spectra were obtained by subtracting the post-edge background from the overall absorption and then normalizing with respect to the edge-jump step. Then the obtained data were Fourier transformed to R space to separate the EXAFS contributions from different coordination shells. The quantitative structural parameters around central atoms, least-squares curve parameter fitting was performed using the ARTEMIS module of IFEFFIT software packages.

H 2 temperature-programmed reduction (H 2 -TPR) was carried out on a Micromeritics
Chemisorb 2920 instrument with a TCD detector. Before each test, the catalyst (50 mg) was pretreated at 400°C for 1 h under the flow of purified Ar (50 mL/min). After cooled down to 50°C, the catalyst was heated to 800°C at the rate of 10°C/min in a stream of 10% H 2 /Ar (50 mL/min). For O 2 temperature-programmed desorption (O 2 -TPD) experiments, the catalyst was first pretreated at 400°C in He flow for 1 h followed by being cooled to 50°C. Then the catalyst was exposed to the stream of 5% O 2 /He (50 mL/min) for 30 min and purged by pure He afterwards for the removal of residual gaseous O 2 . Lastly, the temperature was increased to 850°C at the rate of 10°C/min under a He flow and the signal of desorbed O 2 was recorded by a mass spectrometer (HIDEN, HPR-20 R&D).
For temperature-programmed surface reaction of CB (CB-TPSR), the sample was first performed with similar procedure, except that a flow of pure He was used when temperature was risen up to 900°C and CB signal was recorded.
Pyridine-IR spectra were collected by using a Bruker Tensor Ⅱ spectrometer equipped with a quartz cell connected to a vacuum system. A thin wafer was obtained through crushing the powder catalyst and pretreated at 350°C for 1 h under vacuum. After cooled down to room temperature, the catalyst was connected to pyridine for adsorption (30 min). Then the desorption was carried out under vacuum with temperature rising to 100°C, and the spectra were recorded at 30 and 100°C.
For in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the experiments were conducted in a chamber with BaF 2 windows and the catalysts could be heated to 550°C. Prior to CB oxidation, the catalysts were pretreated at 400°C for 1 h under a flow of nitrogen followed by being cooled to 100°C and the spectra were recorded as background. Then the catalysts were exposed to mixed gas stream (60 mL/min) of 500 ppm CB, 21% O 2 /N 2 and 3 vol. % (when used), meanwhile, the sample chamber was heated and DRIFTS spectra were collected at various temperatures.
As for DFT calculations, the energy cutoff for the plane wave basis expansion was set to  For the calculation of apparent activation energies of catalysts, the reaction rates of each sample show negligible change under the GHSV at 11000 mL·g -1 ·h -1 , 22500 mL·g -1 ·h -1 and 45000 mL·g -1 ·h -1 , indicating that the effect of external diffusion could be eliminated by using GHSV regulation. The particle size of catalysts between 40-60 mesh was chosen for the elimination of internal diffusion. [1] The following Arrhenius equation was used and the CB conversion was controlled to lower than 15%.
where r is the CB reaction rate (mol·s -1 ·g cat.   Note: Figure S5a provides the XPS survey of all catalysts. The La 3d XPS spectra in Figure   S5b contain two main peaks at 834. 1 Figure S6. EPR profiles of as-prepared catalysts. Note: In Figure S8, the IR bands at about 1440 and 1595 cm -1 are assigned to pyridine adsorbed at Lewis acid sites, while the peak at 1550 cm -1 should be related to Brønsted acid sites. [4,5] Another band corresponding to both Lewis acid sites and Brønsted acid sites is observed at 1490 cm -1 . [6] The intensity of adsorption peaks gets weakened slightly when the temperature rises up, which indicates the relative strong strength of acidity on these catalysts.   Note: In Figure S12a, the bands at 3856 and 3745 cm -1 should be assigned to free OH groups of H 2 O, [7] the intensity of which increase with temperature rising. The phenolate species (1603 and 1262 cm -1 ) on the surface come from the CB adsorption via cleavage of C-Cl bond. [8] The vibration peak at 1550 cm -1 is due to carboxylate [9,10] while the bands at 1509, 1458 and 1420 cm -1 are assigned to COO-symmetric and antisymmetric stretching vibration of (chlorinated)-maleates and acetates. [11][12][13] Besides, the bands at 1373, 1335 and 1317 cm -1 can be ascribed to -COOH from bidentate formats. [14] In Figure S12b, the bands at 3386, 3230 and 1649 cm -1 are attributed to hydrogen-bonded OH groups, [15] the bands of which increase in intensity with the rise of temperature. The bands at 1875 and 1696 cm -1 are due to     [16] where ∆E 3s is the binding energy gap between two main peaks of Mn 3s spectra. where IA(L) and IA(B) represent integrated absorbance of Lewis acid bond and Brønsted acid band, respectively, R is the radius of catalyst disk (cm), and W is the weight of disk (mg). [17] [20] Mn-Ce-Zr 1000 ppm CB, 21% O 2 , N 2 30000 h -1 326 385 [21] Pd/LaCoO 3 1000 ppm CB, 21% O 2 , N 2 12000 342 430 [22]